The Effects of Various Factors on Plant Yield.
Yield of commercially valuable species in the natural environment may be suboptimal as plants often grow under unfavorable conditions, such as at an inappropriate temperature or with a limited supply of soil nutrients, light, or water. Increased tolerance to abiotic stresses, such as water deprivation, salt, freezing and other hyperosmotic stresses, and cold, and heat, may improve germination, early establishment of developing seedlings, and plant development. In water-limited environments, crop yield is a function of water use, water use efficiency (WUE; defined as aerial biomass yield/water use) and the harvest index (HI; the ratio of yield biomass to the total cumulative biomass at harvest). WUE is a complex trait that involves water and CO2 uptake, transport and exchange at the leaf surface (transpiration). Improved WUE has been proposed as a criterion for yield improvement under drought. Water deficit can also have adverse effects in the form of increased susceptibility to disease and pests, reduced plant growth and reproductive failure. Genes that improve WUE and tolerance to water deficit thus promote plant growth, fertility, and disease resistance. Enhanced tolerance to these stresses would lead to yield increases in conventional varieties and reduce yield variation in hybrid varieties.
Fortunately, a plant's traits, including its biochemical, developmental, or phenotypic characteristics that enhance yield or tolerance to various abiotic or biotic stresses, may be controlled through a number of cellular processes. One important way to manipulate that control is through transcription factors—proteins that influence the expression of a particular gene or sets of genes. Transformed and transgenic plants that comprise cells having altered levels of at least one selected transcription factor, for example, possess advantageous or desirable traits. Strategies for manipulating traits by altering a plant cell's transcription factor content can therefore result in plants and crops with commercially valuable properties.
We have identified polynucleotides encoding transcription factors, including Arabidopsis sequences G1792, G1791, G1795, G30, soy sequences G3518, G3519 and G3520, rice sequences G3380, G3381, G3383, G3515, G3737, corn sequences G3516, G3517, G3739, and G3794, Medicago sequence G3735, and Triticum sequence G3736 (SEQ ID NOs: 2, 4, 6, 8, 22, 24, 26, 10, 12, 14, 16, 32, 18, 20, 34, 36, 28, and 30, respectively) and equivalogs listed in the Sequence Listing from a variety of other species, developed transgenic plants using almost all of these polynucleotides from diverse species, and analyzed the plants for their tolerance to low nitrogen conditions, tolerance to cold, tolerance to water deficit conditions, and/or resistance to disease. In so doing, we have identified important polynucleotide and polypeptide sequences for producing commercially valuable plants and crops as well as the methods for making them and using them. Other aspects and embodiments of the invention are described below and can be derived from the teachings of this disclosure as a whole.